Switched power converters are circuits having numerous applications in distributed generation (DG) power systems. FIGS. 1-4 depict four types of commonly used switched power converters. FIG. 1A depicts a two level power factor corrected (PFC) rectifier 102. Here, PFC rectifier 102 is used to shape the line currents ia, ib and ic to be proportional to the corresponding line voltages Va, Vb and Vc. FIG. 1B depicts an example graph of the line voltage versus time, and the line current versus time, where j is used to denote a, b or c. Here, it can be seen that the line current ij is kept proportional to the line voltage Vj.
FIG. 2A depicts a two level active power filter (APF) 104, which is another example power converter. Here, APF 104 is used to generate anti-harmonic and reactive currents to suppress or cancel harmonics in the power lines. FIG. 2B depicts an example graph of the system line voltage, Vj, versus time. FIG. 2C depicts an example graph of the line current, ij, versus time prior to adjustment by the APF 104. FIG. 2D depicts an example graph of the anti-harmonic or reactive current, icj, versus time and FIG. 2E depicts an exemplary graph of the resulting line current, ilj, after adjustment by the APF 104.
FIG. 3A depicts a two level pulse width modulated (PWM static volt-ampere-reactive (VAR) compensator (SVC) 106, which is another example of a power converter. Here, SVC 106 is used to generate a 90 degree phase offset, either leading or lagging, of the line current from the line voltage so as to control power flow from a power grid. The power grid is typically a power system, or power utility, which is a network of transmission lines, transformers, loads, power generators, motors and the like. FIG. 3B depicts an example graph of the line voltage, Vj, and the line current, ij, versus time where ij lags Vj and FIG. 3C depicts an example graph of the line voltage, Vj, and the line current, ij, versus time where ij leads Vj. An example of a similar type of power converter is a static synchronous compensator (STATCOM).
FIG. 4A depicts a two level grid connected inverter (GCI) 108, which is another example of a power converter. Here, GCI 108 is used to convert time-static, or direct current (DC), power into time-varying, or alternating current (AC), power flowing into the power grid, where the generated current (ij) has a polarity opposite that of the line voltage (Vj). The power grid is typically a power system, or power utility, which is a network of transmission lines, transformers, loads, power generators, motors and the like. FIG. 4B depicts a graph of Vj and ij versus time, where Vj and ij have opposite polarities. GCI 108 is typically used to convert DC energy from renewable or alternative energy sources such as fuel cells, photovoltaic sources, batteries and the like.
Each of the power converters 102-108 are operating by controlling the state (opened or closed) of each of the various switches 110. Some conventional control methods employ DQ conversion and real-time reference current calculation. These methods require a high-speed digital microprocessor and high performance A/D converters and result in a higher cost, higher complexity and lower reliability. Another conventional control method is referred to as one cycle control (OCC).
OCC is a unified pulse width modulation (PWM) control method that is capable of controlling basic power converters with relatively lower costs, lower complexity and higher reliability. OCC is described in more detail in U.S. Pat. No. 5,278,490, issued Jan. 11, 1994, which is fully incorporated by reference herein. Many previous OCC controllers were not capable of operation with different types of power converters 102-108. The design of separate OCC controllers was required for each type of power converter 102-108.
More recently, OCC controllers were developed capable of controlling more than one type of power converter. For instance, three phase two-level OCC controllers capable of controlling a PFC 102, APF 104 and GCI 108 were described in U.S. Pat. No. 6,297,980 issued on Oct. 2, 2001 and U.S. Pat. No. 6,545,887, issued on Apr. 8, 2003, both of which are fully incorporated by reference herein. However, these OCC controllers were not capable of operation with each type of power converter 102-108.
Accordingly, a universal controller capable of controlling multiple types of two and three level power converters is needed.